1. Field of the Invention
The present invention relates to an induction system for a multicylinder internal combustion engine in which a plurality of port-throttled intake runners is supplied with air by a single unthrottled air log.
2. Disclosure Information
Internal combustion engines typically include one or more throttle plates positioned either as a single throttle plate in an air log upstream of individual cylinder runners or within the individual cylinder runners themselves. If a single air throttle plate is used far upstream of the intake valves positioned at the various cylinders, the pressure of the entire manifold must change if the quantity of air flowing through the manifold is to change in response to an altered throttle angle, as prompted by the operator, whether it be a human operator or, for that matter, an automotive speed control. Of course, any change of the air pressure within an entire intake manifold will be accompanied by a time lag in the response of the engine.
Automotive designers seeking to avoid throttle response problems have produced intake manifolds or induction systems using individual throttle plates mounted at the bottom of the intake runners close to the intake valves. Such a configuration allows good throttle response by limiting the volume of the manifold which is subjected to subatmospheric, i.e., vacuum, pressure. However, if a source of engine vacuum is needed either to draw gases from the engine crankcase as in a positive crankcase ventilation system, or to recirculate exhaust gas, or to operate various vacuum powered devices such as a power brake booster or motors associated with a climate control system of the vehicle, it is necessary to place vacuum taps into the intake runners between the individual throttle plates in the intake valves. One automotive engine marketed by Bayerische Motoren Werke (BMW) utilizes such a scheme, in which an air manifold is connected with individual pipes running to the inlet runners between the individual throttle plates and intake valves. Unfortunately, the BMW system has no control valves located in the individual pipes or branches extending between intake runners and the air manifold. As a result, the pressure within each of the manifold runners is lowered to a vacuum or subatmospheric level because the individual cylinders are interconnected by the air manifold. Because the cylinders are lowered to subatmospheric pressure, the BMW system will operate with a pumping loss that is avoided by a system according to the present invention.